Blender's world environment sky looks flat
You can adjust the coordinates of the Environment texture to manipulate the 'centreline' of the environment. This can be achieved with the following nodes :



Adjust the Mapping node to skew the coordinates in a specific direction. The Normalize node ensures the result is still a valid Normal for the environment texture.

Obviously there are limitations to this since the environment is effectively projected onto an infinite sphere - adjusting too far will noticeably reduce one half of the environment into an ever decreasing circle while stretching out the opposite side.